Fluid metering valves are already known, which comprise a reversible actuator consisting in the association of a direct current motor or gear motor with a cam transformation system to generate a linear movement and control a regulation rate by more or less pushing a valve away from the seat thereof. Such combinations of the state of the art are based on various solutions for motors or gear motors:
A first solution consists in using a direct current motor with a brush combined with a reduction gearing and a cam transformation system to generate the axial displacement of the valve, as disclosed, for example, in the U.S. Patent Publication No. 2012/0285411. This first solution has the advantages of a significant movement reduction and thus an interesting power reserve, simple control using a bifilar connection, the absence of any other smart electronic member. Such solution is interesting as regards costs and capacity to work at high temperatures.
But this solution has two major drawbacks relating to the mechanical switching of electrical signals, which results in the brushes wearing and thus a limited service life, as well as significant electromagnetic emissions which affect the other electronic members nearby. Both drawbacks are more and more a problem for the new specifications of electric actuator for automobiles. On the one hand, always longer service lives are expected from the motors, and on the other hand, the quantity and proximity of electric actuators in motors require a reduction in electromagnetic emissions. Eventually, the spatial configuration of the solution is not very advantageous since it requires positioning the gear motor along an axis perpendicular to the axis of the actuator output member, which leads to a delicate integration on the vehicle engine block.
A second type of solution is based on a torque motor, which is a second (brushless) direct-current motor, which drives a cam device to generate the translation of a valve as disclosed, for example in patent FR2978998. Such solution has the same advantages, as regards a simple control, relative to the bifilar control of the previous solution since it is also based on a direct-current motor, and it additionally takes advantage of the absence of brushes, which increases their service lives, since no brush wears, as compared to the previous solution. Eventually, such solution is thus interesting because of the extended service life and the low electromagnetic emissions resulting from the absence of brushes, because working at high temperatures is possible thanks to the absence of smart and thus binding (as regards cost) electronic components, and because control, which remains bifilar, is simple.
But it also has the drawback of being based on an actuator with a limited travel, which prohibits any kind of reduction in the movement upstream of the cam transformation system, which is a significant obstacle, as regards the maximum forces which can be reached. As a matter of fact, the forces obtained with the second solution are half those obtained with the first family of solutions for a higher power consumption. Similarly to the actuators of the previous family, the perpendicular orientation of the torque motor relative to the output member results in a delicate integration of the actuator, because of the transformation by a cam roller.
Eventually, a third family of known solutions for such reversible actuators for fluid regulation valve control, consists in using an electronically-switched polyphase motor, also currently referred to as a BLOC (for Brushless DC) motor, which corresponds to a brushless polyphase motor, the electronic switching of which, inside the control device, makes it possible to control the electric signals in the phases of the stator, according to the position of the rotor, which is measured by magneto-sensitive sensors. Such motor is associated with a screw-nut transformation system to generate the translation of the valve control member, according to a movement coaxial with that of the motor. In this case, the control device is rather complex, since it works in closed loop, to adapt the signals sent to the stator, according to the actual position of the rotor. Such solution is disclosed in several patents, among which the European patent EP1481459.
Such solution has the advantages of being brushless and thus provides the same guaranteed values of durability and low magnetic emission as the previous solution, but also has a sufficient movement reduction to reach high forces similar to those obtained with the solutions of the first family. Eventually, such configuration is interesting as regards integration since the coaxial nature of the movement of the central screw relative to the motor stator results in a globally axisymmetric construction which greatly facilitates the integration thereof on an engine block and provides an advantageous global compactness of the solution.
On the contrary, this solution requires using complex control electronics integrating smart equipment which have to interpret information from the rotor position sensor to control the phases of the stator accordingly. This results in an expensive solution implemented at limited temperature since the micro-controller which manages the control of the motor is limited to 140° C., which is too low for the new environmental constraints for the valves under the hood of a car.